And so we go to war, the United States, Britain and Australia - alone. George W Bush and Tony Blair see this as a Churchillian moment: alone? So be it. If their troops are received in Basra by surrendering Iraqi soldiers, and by Iraqi civilians cheering their liberators, they say all the rest will be forgotten.

We shall soon know.

We can expect the war to be run with more professionalism than the diplomacy that has led up to the war.

These past two weeks have recalled Freedonia going to war in the film Duck Soup, except that the Marx Brothers meant it to be funny. The lugubrious diplomatic nadir was surely the British proposal that war might be called off if Saddam Hussein went on television to say "sorry".

A final UN resolution and vote were abandoned by the allies, not only because they lacked the votes for a resolution authorising war, but also because they faced the possibility of a majority vote against them - sending them to war in actual defiance of the security council.

The problem was not the French veto. The US and Britain had already said they would be satisfied with a "moral victory," a majority vote the French were forced to veto. The allies were blocked by concern that Angola, Chile, Pakistan, Cameroon, Guinea and Mexico might vote against them. This inability to persuade , intimidate or bribe friendly or dependent countries on a matter so vital to the US government is unprecedented in postwar history.

Washington has even had great difficulty in getting Nato's Turkey to open itself to US forces. To force this still unsettled issue could provoke a crisis for Turkey's democracy, making Turkey, in this war, the first victim of friendly fire.

The failure of the US to win international support for its position on Iraq is due in part to the weakness of its case. Few saw Iraq in its present condition as a threat to anyone, much less to the US.

Washington had no serious evidence linking Iraq to al-Qaida. The failure was also due to this administration's arrogance in its employment of American power.

However the hostility was already there, latent. It was there because history says that use (or abuse) of hegemonic power inspires challenge. The resistance may arise hesitantly, but a crisis can provoke convergence or consolidation of the individual elements of resistance, so that each reinforces the others. This is what has happened.

Germany's initial rejection of the war was the act of a politician in electoral trouble, responding to public opinion. It probably would have been unimportant had the US not reacted as it did, and had Jacques Chirac not supported the Germans. Doing so, he catalysed international opposition to American unilateralism. France, moreover, offers the only coherent and relevant modern model of constructive resistance to US power: the Gaullist model. Articulated in the security council debate, this found overwhelming support in international opinion.

The result has been a basic shift in international relations, which will affect the future configuration and policies of the EU, no matter what happens in Iraq. Closer union and a common defence formerly seemed luxuries. This no longer seems the case.

A similar development, less advanced, is taking place in the Far East, caused by a US policy toward North Korea that does not have the support of South Korea, Japan or China.

Something has happened that might be compared with the breakup of the Austro-Hungarian empire in 1918. Before the first world war, tensions existed inside that empire, but the aura of benevolent imperial authority was intact, and the troubles could be contained.

The war, and Woodrow Wilson's doctrine of universal national self-determination, destroyed the aura, and the authority, of the empire, with results that contributed heavily to the outbreak of a second world war.

The war in Iraq is intended to establish US authority over the Middle East. But Washington never imagined that it would be successfully challenged in Europe and the UN.

If the Bush administration's optimism about the course of the Iraq war proves correct, America's international authority will provisionally be re-established. But the aftermath, as the US tries to control Middle Eastern developments, will automatically generate new forces of resistance and hostility.

We will still find ourselves in post-imperial disorder. The American superpower has been the centre of a solar system. Centrifugal political forces now have been set loose. These will be extremely difficult for Washington to deal with, so long as it remains on its global course.

They may also prove more dangerous than Washington, or anyone else, now thinks.